The present invention relates to a means for joining a ceramic shaft with a metallic shaft, especially for use in such devices as turbochargers and gas turbine rotors.
FIGS. 1 to 4 show conventional structures for joining a metallic shaft to a ceramic shaft. In FIG. 1 the end portion of a ceramic shaft 1 has a smaller diameter than the remaining portion thereof. The end portion to be connected is inserted into the tubular end portion of a metallic shaft 2 and affixed by means of a shrink fit. In FIG. 2 the end of a metallic shaft 2 has a larger diameter than the remaining portion thereof and it is provided with a hole for receiving the end portion of a ceramic shaft 1 to be connected. The end portion of the ceramic shaft 1, is inserted into the hole and affixed by means of a shrink fit. In FIG. 3 the end portion of a ceramic shaft 1 is joined with the end portion of a metallic shaft 2 through a brazing alloy layer 3. In FIG. 4, the end portion of a ceramic shaft 1 is inserted into a hole provided at the end portion of a metallic shaft 2, similar to that depicted in FIG. 2. The end portion of the ceramic shaft 1 is joined by using a brazing alloy layer 3.
According to the conventional joint structures thus constructed, the portions of the ceramic shaft 1 and the metallic shaft 2 to be joined are heated to a high temperature to obtain the shrink fit. Therefore, the mechanical strength of the tubular portion of the metallic shaft 2, having such a thin section can result in mechanical distortion. Furthermore, the end portion of the metallic shaft may be exposed to high temperatures during use. As a result the end portion expands in the radial direction thereby eliminating the shrink fit and allowing the ceramic shaft to separate from the metallic shaft. Furthermore, in case of using the brazing alloy layer, the brazing alloy layer may be oxidized thereby reducing the strength of the connection.